i was told that you can make a 90hp elpto and put bigger carbs on it and mess with the gear ratio and you will have a 115 or a 125 is this true?

way2slow can probably help here. I know my Yammie 150 ProV is merely a restricted 200 ProV and can be upgraded by adding on about $1200 worth of carbs, reeds and an exhaust tuner.  

On some motors, it's like cart7 says, for instance the only difference between the 3L OMC 200's and 225's is the carbs.  On other motors it's a lot more complicated than that.  You can get into things like different exhaust tunners, different port timing, different bore size, different induction system and on and on.

From the model number, that sounds like a 90 hp merc and I'm not much on the black motors so can't really help you with one of them.  It could be just the carbs, it could be much more.  I know the 135 carb motor and the 150 carb motor, the only difference is the carbs on those two.  This is your best source of info for the merc motors,  http://forums.screamandfly.com/forums/forumdisplay.php?f=20

On the V-4 90 hp OMC's, its what I mentioned above.  The 115 has different exhaust system, different porting and I think bigger carbs so it's not pratical to try and change a 90 to a 115.

well i gusse you cant do it i was told you can with a four stroke but the ELPTO in not a 4 stroke its a 2 so i dont think you can

actually, Big Al's reply was a little confusing.  What he said was the 115 is a four cylinder motor and your 90 is only a three cylinder motor.  Now, if you could come up with a way of adding another cylinder, you might be able to do it.

Four strokes are actually the hardest to modify, if not almost impossilbe.  Behind them are the DFI two strokes, they can be but it takes big bucks and someone with the know how and willing to violate EPA laws against messing with them.  The carb'd two strokes are the easiest.  Some motors much easier than others as I mentioned above.  Where you see real gains in two strokes is when the use the same motor for a number of different hp's.  For instance you 90 is basically the same as the 75 so usually with just a little work, you can make a 75 and 90.  However, you 90 is already near the limit for that block's available power for a stock, all around use motor.  To get any more, would require porting and other mods to raise the rpm and power band.  Get it up to about 8,000 - 9000 rpm and it might make 125 hp, but would have a hard time getting more than an empty jon boat up to speed to use all that rpm.

oh ok that clears it up thanks